1. Field of the Invention
The present invention relates to information technologies, and relates in particular to an apparatus for quickly accessing information stored in any specific recording layer in an ultra-high capacity storage device based on laminated holograms, a recording medium for information storage and a method of accessing the information and an illumination head for use in such a recording apparatus.
2. Description of the Related Art
There has been a growing need for compact, high capacity memory devices to meet the demands of mobile computing devices and other similar data storage devices. The simplest card type memory device currently in use is a magnetic stripe bonded to a card base, but because of its inherent small memory capacity, they are only useful in a limited number of applications.
FIG. 23 shows an example of the card type IC memory device xcex5 having a higher memory capacity than the magnetic card. Such a device xcex5 is comprised by embedding a memory element, such as ROM and flash ROM, in an IC card medium 23, and is supported by a card guide 24 provided on a data accessing device. Data are read from or written in the memory element by contacting a read/write electrode 25 with a read/write head 26 provided on the accessing apparatus.
However, in the case of the conventional IC cards, although the memory capacity is higher than the magnetic cards, it is still insufficient to meet the future requirements for increasing the memory sizes to several hundred megabits to several gigabits. Costs of bits in such devices are also high and, therefore, they are not suitable as practical future high capacity memory devices.
FIG. 24 shows another example of a similar IC card 101 to be processed by a reading apparatus comprised by a read head 102, electrodes for read or write functions, and guide rollers 104 for positioning the IC card 101. Compared with the magnetic cards, their memory capacity is much higher but is still insufficient to meet the needs of mega to giga range of bit memory capacity. This device is also not suitable for future high capacity memory device because of the high costs for making a three-dimensional architecture required for uses in multilayer devices and information input/output circuits.
It has been suggested that higher memory capacities can be realized by using holograms to record information. Hologram recording is anticipated to be a likely future medium for software distribution because of the low unit cost of bits as well as the difficulty of counterfeiting. In particular, planar hologram ROMs can be mass-produced using a printing technology, and a further increase in the density of recording volume is possible through the use of a holographic card in which a planar hologram is embedded in a waveguide and the data are replicated from one specified layer using waveguided light as reference light (refer to a Japanese Patent Application, Second Publication, Hei 10-32578).
In the holographic data storage method, a multi-layered waveguide recording medium is produced by alternating a core layer and a clad layer, and information is recorded as scattering centers in each waveguide layer. Desired information can be reproduced by coupling an input light with a target waveguide layer to reproduce only the desired hologram image. This technology presents a distinct feature that the card medium can be structured such that other waveguide layers are prevented from coupling, thereby suppressing the chances of cross talk.
FIG. 25 shows an example of a candidate for the high capacity holographic memory card 105, containing multi-layered ROM devices of ten to several tens of micrometers interlayer spacing The card type recording medium 105 includes a plurality of recording layers 106, each layer having a wedge-shaped hologram (ROM) to be read as a hologram image H out of the layer (actually, on both surfaces of the layer) when an illumination light is injected from a wedge tip 106a. The hologram image can be read at highspeed by a solid-state recording device 107.
The information recording card 105 can be manufactured by a relatively simple process of laminating the hologram recording layers 106, resulting in increasing the thickness of the data storage section and the memory capacity.
However, it is necessary for this recording card 105 to be able to produce a hologram image from a specific layer of the laminated structure, by focusing the beam L precisely at a definable hologram layer of the card medium, so as to propagate and scatter the input light within that layer only to produce the desired hologram image H while avoiding a cross talk between the layers.
For this purpose, the beam spot La of the light beam L is not only required to focus on the light injection end 106a (base of the wedge) but also to move on one axis in the thickness direction of the card medium 105, as well as to be able to move in the x and y directions as shown in FIG. 25. As illustrated in FIG. 25, the card medium 105 is scanned in the x, y directions quickly and smoothly by a beam spot La, generated from a light source 108, to focus the light through a lens 100 of an optical system 109 on the specific layer of the multilayer card medium 105.
FIG. 26 shows another example of the IC card. This IC card 201 is similar to the IC card 101 shown in FIG. 24, and it is still insufficient to hold data in the range of several hundred mega bits to giga bits, and considering the difficulty of producing a laminated magnetic card in three-dimensions and the high cost of bits, there is little practical potential for this design.
FIG. 27 shows another example of a high-capacity memory medium in the form of a hologram card 203, comprised by a lamination of hologram patterns spaced apart at about several tens of micrometers, recorded in wedge type recording layers 241. Input light is injected from the base of the wedge and a hologram image is produced on both sides of the memory section, and is recorded with a solid state imaging element 205.
The hologram card medium 203 can be made by laminating recording layers, and each recording layer produces a two-dimensional hologram which can be transmitted quickly. In this system also, the beam spot La must be moved in three-dimensions to access data recorded in individual recording layers.
The primary problem in such systems is the precision required in the complex movement of the beam spot La in a three-dimensional space, at sub-micron precision to obtain the required degree of recording density. For this reason, such systems have not been practical for the needs of high speed data transmission.
Although a potential for low cost recording has been indicated by the use of holographic recording technology, some of the important basic needs have not been properly addressed in this technology. For example, it is necessary to couple the light to a specific waveguide layer in order to access data recorded on this specific waveguide layer, but presently, neither the method of simple detection of the coupling state between the input light and the waveguide layer nor the method of targeting the specific waveguide layer has been established. Without having such basic techniques firmly in place, it is not possible to establish highspeed accessing to reproducing the data or to devise a practical compact device at low cost.
The holographic technology is used sometimes to prevent counterfeit card as disclosed in a Japanese Patent Application, First Publication, Hei 7-306630. Counterfeit cards can be identified by checking for a hologram image that contains machine readable information recorded on the card medium as well as a decorative hologram image not containing any hard information. However, conventional hologram cards can only record information on one layer only, so that a high capacity memory requires a large recording area. To increase the memory size, a multi-layered card is necessary, but to use such a laminated holographic card for practical purposes, it is important to be able to accurately access a desired hologram in the laminated holograms, and presently, a technology for focusing a beam of light on definitive positions in such a multi-layered information medium has not been established.
It is, therefore, a first object of the present invention to provide an information recording medium and an information reading apparatus that can detect the coupling state of the input light to a waveguide in the laminated information recording medium in a simple manner, so as to enable to focus the input light on a target recording layer to access the information recorded in the target recording layer accurately and quickly. The apparatus should also be compact and economical to produce.
A second object of the present invention is to provide: an apparatus for reading and transferring information at high speeds; quick access to information; a high capacity information recording medium for the apparatus; and a method for high-precision aligning of input light to a target recording medium. Manufacturing of the apparatus and the recording medium having an ultra-high data storage capacity should be simple and low cost. Highspeed access to information is enabled by developing a simple method of aligning the illumination head with a target recording layer.
A third object of the present invention is to provide a hologram reading apparatus and a method for high-precision aligning of input light to a specified hologram recording layer efficiently and at low cost while enabling to retain all the advantages of holographic recording of information.
A fourth object of the present invention is to provide: an information recording medium that is capable of ultra-high capacity data storage and reliable outputting of data; an information reading apparatus for reliable reading of information recorded in such a medium; and a method of using the information reading apparatus.
These objects have been achieved by developing a method for reading a target hologram so that the input light can be accurately directed to a target hologram contained in a hologram element comprised by a laminated planar waveguide type recording layers, by detecting the light emitted from the recording layer, judging the results and counting the results, so that data from the target recording layer can be read by directing the input light according to the data in a servo information image and other judging results.
In more specific details, the objects have been achieved in the hierarchical concept embodied in the succeeding apparatuses and methods that are briefly explained.
An apparatus for selectively reading data recorded on an information recording medium formed by laminated recording layers, comprises: a light source for injecting a light on an input edge of a lamination recording section, of a multi-layered planar waveguide type, assembled into the recording medium containing laminated recording layers, each recording layer having data represented by scattering centers; a converging lens for freely adjustably focusing the light emitted from the light source to generate an input light; an input light directing device for directing the light source and the converging lens as a unit so as to focus the input light to a desired location; an image recording device having an imaging element for recording an informational image generated by diffraction effects of guided waves produced within the multi-layered planar waveguide type recording element; an optical power detector for detecting output light emitted from an output edge of a recording layer as well as scattered light generated from layers other than the recording layer; and an optical power discrimination circuit, operatively connected to the input light directing device, for determining whether an optical power detected by the optical power detector is associated with the output light or the scattered light.
The present apparatus enables to access data recorded in any specific recording layer quickly and simply by focusing input light on a core layer of a multi-layered hologram recording card medium.
Because the absolute positional information is minimized, data storage capacity of the card medium is almost unaffected while enabling to make the apparatus compact and low cost.
An apparatus for reading data in an information recording medium containing a plurality of lamination recording sections arranged longitudinally and separated by a plurality of longitudinally extending head seek grooves, is comprised by: an illumination head device having a light output section shaped to freely couple or decouple from a head alignment groove formed at a light input section of each of the lamination recording sections, and to freely slide in a thickness direction of the information recording medium when being coupled with the head alignment groove for aligning with a recording layer; and an image data recording device having an imaging element for recording a floating image formed in a space above the information recording medium generated by output light emitted from the illumination head device interacting with a lamination recording section.
According to the above apparatus, control mechanisms for selecting a target recording layer in the laminated holograms and control sequence are simple but effective, thereby providing an apparatus that can seek/access information quickly at low cost.
Another apparatus for reading data recorded on lamination recording sections, having multi-layered recording layers within each lamination recording section, embedded in a ring shape and held integrally in a data storage disc, is comprised by: optical system means for focusing an input laser light on a light injection window of a target recording layer in the data storage disc; reflected return light detecting means for detecting a returning portion of the input laser light reflected from a lamination section; separator/comparator means for separating and comparing frequency components contained in photo-electric converted signals produced by the reflected return light detecting means; counting means for counting a number of traverses made by the photo-electric converted signals across a predetermined threshold value; and aligning means operatively connected to the separator/comparator means for aligning the input laser light with the light injection window by moving in an axial direction.
According to the above apparatus, the disc has a ring of lamination recording sections to be read by illumination from inside periphery of the disc attached to the center shaft which is driven by a solid motor, aligning of input light with the light injection window can be performed by a uniaxial movement of the center shaft at right angles to the card medium. This design facilitates access to the target recording layer at low cost.
Another apparatus for reading information recorded on a target waveguide by injecting an input light into a lamination recording section comprised by a plurality of waveguides serving as information recording layers in an information recording medium is comprised by: an extreme layer detection device for determining positions of a front waveguide and a rear waveguide in the lamination recording section; a layer edge detection device for determining positions of a front waveguide edge and a rear waveguide edge; and a layer position determining device for determining positions of each waveguide and a slanted surface associated with each waveguide edge, according to positions of the front waveguide and the rear waveguide obtained by the extreme layer detection device and positions of the front waveguide edge and the rear waveguide edge obtained by the layer edge detection device.
According to the above apparatus, the positions of the recording layers in the lamination recording section can be obtained from the positions of the front and rear recording layers and the input edges of the waveguides. Therefore, the apparatus can provide data in the target waveguide quickly and reliably by a few simple steps of identifying the positions of waveguides and slanted input edges from a lamination recording section containing many waveguides.
Also, according to the above apparatus, horizontal position of input edges of all the waveguides for focusing input light can be detected reliably so that fluctuations in the waveguide position can be accommodated without the loss of precision even when the number of waveguides is increased.
An information recording medium is structured as a card medium having card framing to contain not less than one longitudinally extending lamination recording section comprised by planar waveguide type information recording layers laminated in a thickness direction of the card medium and a row of head alignment grooves having respective light injection windows separated by a head seek groove extending longitudinally so as to permit an illumination head to freely travel in the head seek groove to couple with a desired light injection window.
According to the above information recording medium, a basic section is a lamination recording section produced by vertically piling a plurality of planar waveguide type recording layers containing holograms (ROM layers). Therefore, only the light injection windows need to be fabricated precisely in the form of head aligning v-notches. These notches can be fabricated all at once, after laminating the recording layers, so that ultra-high capacity memory device can be mass produced at low cost, thereby presenting a significant advance in the state of the art of memory devices.
Another information recording medium is comprised by a data storage disc section having recording sections comprised by a lamination of recording layers distributed in a ring shape and a support section for supporting the data storage disc section at its periphery.
According to the above recording medium, a desired number of recording layers are piled successively and the assembly is fabricated together into a data storage disc, so that the ultra-high capacity memory medium can be manufactured easily at low cost, thereby presenting a significant advance in the state of the art of memory devices.
Another information recording medium is comprised by a lamination of a plurality of waveguides serving as recording layers, and containing markers indicating a position of a light injection window corresponding at least to a front recording layer and a rear recording layer.
According to the above recording medium, the position markers for the front and rear recording layers enable input light positions in three-dimensions to be identified readily so that precision alignment can be performed quickly.
A method for selectively reading data recorded in a lamination recording section comprised by planar waveguide type recording layers by identifying a target recording layer by moving input light across input edges and detecting optical power of output light emitted from output edges to identify the target recording layer and obtaining an informational image to read target data contained in the target recording layer.
This is the basic conceptual approach to the method of reading hologram information. More detailed methods for selecting a target recording layer are described in the following.
A detailed method for selectively reading data from a target recording layer included in a lamination recording section having planar waveguide type recording layers, comprises the steps of:
focusing a light emitted from a light source to form an input light for injecting into an input edge of any of the recording layers including the target recording layer; focusing light on a front recording layer or a rear recording layer serving as references for determining positions of recording layers; focusing light on the target recording layer and detecting an optical power level received on optical power discriminating means; judging whether the optical power level corresponds to output light emitted from an output edge of any one of recording layers or to scattered light produced from layers other than the recording layers while moving the input light across input edges to identify the target recording layer; focusing the light on an input edge of the target recording layer in final positioning to generate an informational image; and recording the an informational image so as to read data contained in the target recording layer.
Another detailed method for selectively reading data from a target recording layer included in a lamination recording section having planar waveguide type recording layers, comprises the steps of:
focusing a light emitted from a light source to form an input light for injecting into an input edge of any of the recording layers including the target recording layer; judging whether the optical power level corresponds to output light emitted from an output edge of any one of recording layers or to scattered light produced from layers other than recording layers, so that, when output light is detected, recording an informational image produced by that recording layer as positioning reference for other recording layers, and, when scattered light is detected, the input light is re-focused to any neighboring recording layer and recording an informational image produced from the neighboring recording layer to obtain data from the neighboring recording layer as positioning reference for recording layers; identifying position of the target recording layer while moving the input light across input edges and judging optical power levels; and transferring the input light to an input edge of the target recording layer, and recording an informational image generated to read data contained in the target recording layer.
According to these detailed methods, selection of a core layer for obtaining hologram data recorded in the core layer can be performed quickly and easily because any target recording layer can be identified by following a simple process of preliminary determination of layer positions followed by precision input alignment with the injection widows of respective target recording layer.
Another detailed method for aligning an illumination head for reading information recorded in a laminated information recording medium, having a plurality of data recording layers laminated in a thickness direction of the card medium, comprised by a plurality of lamination recording sections arranged in a longitudinal direction, wherein each lamination recording section has a head alignment groove at a transverse end for coupling with an illumination head having light injection windows for aligning the illumination head with a specific recording layer by sliding in a card thickness direction within the head alignment groove, and rows of lamination recording sections are separated by longitudinal head seek grooves; the method comprises the steps of:
detecting head positioning markers provided on a longitudinal frame of the card medium to correspond to head alignment grooves; decoupling an illumination head from a head alignment groove and placing in a standby position, and moving the illumination head along a head seek groove to oppose a selected head positioning marker for preliminary head positioning; positioning the illumination head to a top or bottom window position within the head alignment groove, and coupling to the head alignment groove in a vertical position; performing rough positioning of the illumination head so that input light is roughly in line with a target light injection window; and performing precision positioning of the illumination head so that input light is precisely aligned with the target light injection window.
Another method for aligning an illumination head for reading information contained in an information recording medium comprised by a data storage disc section having lamination recording sections distributed in a ring arrangement, is performed by initial alignment based on power levels of reflected return light produced by a portion of input light from a vicinity of input light window of the target recording layer.
Another method for reading data, recorded in laminated information recording medium having a plurality of waveguides as information recording layers, comprises the steps of: detecting positions of a front waveguide and a rear waveguide as well as input edges associated with each waveguide; determining positions of each waveguide as well as the input edges according to positions of the front waveguide and the rear waveguide as well as slanted edge surfaces associated with the input edges; and focusing light on an input light position determined by a position of a target waveguide and a position of a slanted edge surface associated with the target waveguide so as to read data contained in the target waveguide included in the plurality of waveguides.
Another method for aligning an illumination head for reading information recorded in a laminated information recording medium by coupling with an illumination head; the method comprising the steps of:
detecting head positioning markers provided on a longitudinal frame of the card medium to correspond to head alignment grooves; decoupling an illumination head from a head alignment groove and placing in a standby position, and moving the illumination head along a head seek groove to oppose a selected head positioning marker for preliminary head positioning; positioning the illumination head to a top or bottom window position within the head alignment groove, and coupling to the head alignment groove in a vertical position; performing rough positioning of the illumination head so that input light is roughly in line with a target light injection window; and performing precision positioning of the illumination head so that input light is precisely aligned with the target light injection window.
Another method for reading data, recorded in laminated information recording medium having a plurality of waveguides as information recording layers, comprises the steps of:
providing positioning markers to correspond with positions of light injection windows associated with a front waveguide and a rear waveguide; detecting light input positions for inputting light into the front waveguide and the rear waveguide with reference to respective markers; obtaining light input positions to each waveguide in the plurality of waveguides according to detected light input positions of the uppermost waveguide and the lowermost waveguide; and focusing light on an input light position determined by a position of a target waveguide so as to read data contained in the target waveguide included in the plurality of waveguides.